Grinding while pumping a mixture containing liquid and entrained solid and semi-solid matter is a concept which has been known and practiced. However, current grinding pumps only grind and pulverize matter at the upstream end of the grinding pump, in a region between the surface of a rotating comminutor and the interior surface of the grinding chamber. After the mixture has been shredded and pulverized, it is moved along to a pumping section where an impeller forces the liquid and the entrained matter out towards an outlet port. Despite the apparent success of these pumps in the industry, they are not very efficient. Notwithstanding the current methods and devices used in the industry, it is perceived that the efficiency of these pumps has not reached its full potential. Therefore the need exists for still further improvement in the efficiency of grinding pumps, by for example increasing the rate of flow of the liquid and the entrained matter as well as by decreasing the energy requirements as would be readily apparent from a reduction in the required operating rpms.
The object of the present invention is to provide an improved grinding pump capable of pumping liquids containing entrained solid and semi-solid matter, such as raw sewage and the like, while reducing energy requirements and increasing efficiency. The discovery underlying the present invention is the realization that by incorporating the use of serrated edges on the outer edges of the centrifugal pump impeller vanes in cooperation with a serrated interior surface, liquid containing entrained solid and semi-solid matter can also be shredded and pumped by the impeller vanes with less energy and higher efficiency. The discovery is contrary to commercially known prior art teachings that require substantially more energy, exhibit a low efficiency, and limit grinding to the comminutor. The present invention is therefore a substantial improvement as apparent in its efficiency rating of approximately 20%. For the purpose of this application, efficiency is defined as: ##EQU1##
Moreover, in order to achieve an efficiency of 20%, the present invention optimally operates in the range of 900-1200 rpms. Such an operating range is unlike other known commercially available grinding pumps which operate at a higher rpm and achieve a lower efficiency.
Accordingly, the present invention relates to a grinding pump for pumping liquids with entrained solid and semi-solid matter comprising: a housing structure having a chamber with a longitudinal axis, said chamber having an inlet port, an intermediate portion defined by an irregular wall surface of revolution, an eccentric portion having an irregular wall surface and an outlet port; a rotatable shaft disposed along said longitudinal axis within said chamber; a comminutor mounted on said shaft within the intermediate portion of said chamber for rotation with said shaft, said comminutor comprising, a helical blade mounted on said shaft and rotatable therewith, the outer edge of said blade being irregular and when rotating defining a complementary surface of revolution to said surface of revolution of said intermediate portion of said chamber wall and closely spaced therefrom, said blade and said surface of revolution defining means for cutting, grinding and urging said matter downstream; a centrifugal pump impeller including at least one vane, said impeller being mounted on said shaft and rotatable therewith, the impeller being located immediately downstream from said blade, and said vane having an irregular edge which when rotating defines a surface of revolution complementary to a portion of said eccentric portion of said chamber and being closely spaced therefrom, said vane and said portion of said eccentric portion of said chamber together defining a second means for cutting and grinding said matter. As used herein, the word "irregular" is not intended to be limited to randomly variable. It is the intention of the applicant that the expression "irregular edge" means an edge having a plurality of projections, that is non-linear and varies from the linear either in a regular periodic or random fashion. Included within the term irregular edge are projections such as saw toothed edges, square toothed edges and serrated edges whether the periodicity of the variations in such edges is constant or varying.
Preferably the irregular chamber wall is provided by an overlay or liner secured to said housing structure along the wall of said chamber, and said liner including one or more shredding liner segments having a surface which is complementary in shape to the surfaces of revolution defined by said comminutor and impeller when rotating. Means are provided for removably securing said liner within said chamber so as to preclude said liner from rotating within said chamber in response to rotation of said shaft; and means for rotating said shaft within said chamber, such as, for example, a motor are also provided.